1. Field of the Invention
The present invention relates to a battery pack, and more particularly to a multi battery pack system composed of a plurality of battery packs, its control method, and a battery pack using the same.
2. Description of the Related Art
Generally, a portable electronic device such as a cellular phone, notebook or digital camera employs a battery pack including a plurality of chargeable cells as a power source.
In recent years, a multi battery pack system having a plurality of battery packs connected in parallel has been proposed, which provides so sufficient capacity to ensure stable operation of the portable electronic device and allows application to various kinds of portable electronic devices.
However, the multi battery pack system has a problem of difficult control since it is configured so that the number of battery packs included therein is changeable.
In order to solve the problem, various schemes have been proposed. For example, Japanese Patent No. 3405526 discloses a multi battery pack power unit. In the multi battery pack power unit, each of the multiple battery packs include a plurality of cells and a circuit for detecting a charging/discharging state and controlling the charging/discharging, wherein one battery pack is set as a master battery pack and the other are set as slave battery packs. The master battery pack requests transmission of data indicating the charging/discharging state to the slave battery packs by means of communication, manages whole data, determines the charging/discharging state, sends a command, and controls the charging/discharging. On the while, the slave battery packs send data indicating the charging/discharging state according to the data request, receive the command, and conduct the charging/discharging.
According to the above document, the master battery pack controls charging/discharging of the plurality of slave battery packs. Thus, as the number of slave battery packs is increased, more loads are applied to the battery pack set as a master.
Accordingly, there is an urgent need for a multi battery pack system, which is capable of allowing control of numerous slave battery packs without increasing loads on a master battery pack.